1. Field of the Invention
The invention relates to an oil pressure control device that carries out a treatment of discharging foreign matters that have mingled in a circuit, and more particularly, to an oil pressure control device for carrying out a foreign matter discharge treatment for a plurality of solenoid valves.
2. Description of the Related Art
In each of various oil pressure control circuits, a solenoid valve such as an electromagnetic proportional control valve or the like, which operates a valve body with the aid of a solenoid in order to control the pressure of a working fluid for actuating a group of actuators, is employed. The pressure and flow rate of the working fluid that are required for actuation of the actuators are ensured by, for example, operating another control valve using an output pressure of the solenoid valve as a pilot pressure. When foreign matters mingle in an oil pressure control circuit, the valves and the like cannot operate normally. Therefore, contrivances have been made to discharge those foreign matters reliably. Foreign matter discharge control is indispensable especially in the case of a solenoid valve that has an electromagnetically driven valve body and requires accurate oil pressure control.
As this type of oil pressure control device, there is known an oil pressure control device that is equipped with solenoid valves and pressure control valves to control the pressure of a working fluid for an actuator for pulley portions (sheaves) in, for example, a belt-type continuously variable transmission for an automobile, and that is designed to control a line pressure by controlling the current supplied to the first solenoid valve for supplying a pilot pressure to the one of the pressure control valves which has the function of a regulator, and regulate/control the pressure of the working fluid for the actuator by controlling the current supplied to the second solenoid valve for supplying a pilot pressure to the one of the pressure control valves which performs the function of a pressure reduction valve using the line pressure as an original pressure. In this device, a valve plunger is moved in a reciprocating manner by varying the current command value for each of the solenoid valves. Thus, foreign matters deposited on a drain port side can be discharged, and a substantial decrease in circuit pressure on an output port side can be prevented from being caused when those foreign matters are discharged (e.g., see Japanese Patent Application Publication No. 2005-54970 (JP-A-2005-54970)).
There is also known a control device for an automatic transmission that changes over the engagement pressure of an input clutch between a first engagement pressure based on a line pressure and a second engagement pressure during neutral control which is based on a control pressure at a linear solenoid valve, and limits the engagement pressure of the input clutch at most to the first engagement pressure, which corresponds to a minimum line pressure, in performing foreign matter discharge control for the linear solenoid valve during a stop of a vehicle and before the start of neutral control, thereby reducing a shock resulting from fluctuations in the engagement pressure of the clutch during foreign matter discharge control (e.g., see Japanese Patent Application Publication No. 2004-183715 (JP-A-2004-183715)).
Moreover, there are known a valve control device for an internal combustion engine that allows foreign matters that have been stuck in an oil pressure control valve to be discharged without making variations in valve timing, by changing the current applied to an oil control valve (OCV) alternately to a maximum value and a minimum value when there is a request to clean the foreign matters during a stop of an engine with no change in the phase of a valve timing mechanism (e.g., see Japanese Patent Application Publication No. 2001-234768 (JP-A-2001-234768)), and a control apparatus for an automatic transmission that suppresses a shift shock or the vibrations of a clutch caused during the discharge of foreign matters that have entered a pressure control valve, by supplying a dither current with a large amplitude to a linear solenoid so as to remove the foreign matters when it is determined that the linear solenoid and a clutch oil pressure chamber do not communicate with each other through an oil supply passage (e.g., see Japanese Patent Application Publication No. 11-82724 (JP-A-11-82724)). In the case where stable control is constantly required during the driving of an automobile as in the case of line pressure control or the like, when an output port simultaneously communicates with a supply port and a drain port at the time of pressure regulation, a deficiency in the capacity of an oil pump or destabilization of line pressure is caused. Therefore, a so-called overlap-type linear solenoid valve with an output port that is shut off from one of a supply port and a drain port when being brought into communication with the other is used (e.g., see Japanese Patent Application Publication No. 4-171509 (JP-A-4-171509)).
However, in an oil pressure control device as mentioned above, the load applied to an object controlled by a second control valve is minimized when the pressure of a working fluid for an actuator is regulated and controlled by the second control valve using a line pressure from a first control valve as an original pressure. Nonetheless, in the case of a circuitry in which a first control valve is controlled with a pilot pressure from a first solenoid valve and a second control valve is controlled with a pilot pressure from a second solenoid valve, when a foreign matter discharge treatment for the first solenoid valve is carried out during a foreign matter discharge treatment for the second solenoid valve, a considerable load is applied to an object controlled by the second control valve. For this reason, the foreign matter discharge treatment needs to be carried out separately for the plurality of the solenoid valves. As a result, there is a problem in that the foreign matter discharge treatment is time-consuming.
Therefore, in the case where foreign matter discharge control is performed prior to, for example, neutral control of a vehicle mounted with a continuously variable transmission, a sufficient time cannot be ensured for neutral control. In consequence, there is a problem in that an effect of improving fuel consumption through neutral control is lost as well.